By the way, very good work with the optocouplers, and finding the similar Migatronic circuit diagram !!
Looking at that circuit, the reason why the Contactor and the gas valve can work on AC is because they are switched by a Triac on the board - the IT46. This device can switch an AC load, as opposed to a power transistor which is DC only.
Maybe one of the 2N3055 drives the motor forward, and the other shorts it to act as a brake and stop the wire instantly.
Jorva,
Going back to your first post, when you say the wire feed runs all the time does the wire speed control work or does it run at one speed regardless of where you set the speed? If that circuit diagram posted above is relevant to your welder then that may help to narrow down the fault a bit.
Regards
Neil
i just had a look at the pcb and i hav noticed something the long brown 18R wire coiled resistor that has swollen up that i mentioned ealier is conected to the base of one of the 2N3050 transitor and on the other side it goes to a BD 138 10 transistor coud these be the faulty ones?
Measure across the two resistor terminals with your multimeter set on ohms, what do you see as a measurement? POWER OFF of course!! I'll come back to you shortly with the other tests